The present invention relates to an impact-resistant thermoplastic resin composition. More specifically, it relates to an impact-resistant thermoplastic resin composition having excellent processability, transparency and appearance properties. This resin composition is prepared by mixing a butadiene-styrene-methyl methacrylate-alkyl acrylate graft copolymer (hereinafter referred to as an MBAS resin) with a methyl methacrylate-styrene copolymer (hereinafter referred to as an MS resin), the MBAS resin being prepared by postpolymerizing styrene, a methacrylate, an acrylic acid alkyl ester having 2 to 8 carbon atoms in the alkyl group and, if necessary, a crosslinkable monomer copolymerizable with these monomers with a latex of polybutadiene or a butadiene-styrene copolymer comprising mainly butadiene.
There has heretofore been known a thermoplastic resin composition having satisfactory transparency and excellent impact resistance which comprises the MS resin blended with an MBS copolymer or ABSM copolymer (acrylo-nitrile-butadiene-styrene-methyl methacrylate copolymer) which is obtained by graft polymerizing a monomer selected from the group consisting of styrene, methyl methacrylate and acrylonitrile with a butadiene-styrene copolymer (e.g., as disclosed in Japanese Examined Patent Publication No.52-32772). In fact, these thermoplastic resin compositions are transparent and have high impact resistance. However, the appearance properties of these resin compositions are not always satisfactory. A methyl methacrylate resin or a methyl methacrylate-styrene resin is essentially characterized by high transparency and the flaw-free surface and high surface gloss of a shaped article derived therefrom. Because of these characteristics, these resins are advantageously used in various applications. However, in order to overcome the inadequacy, i.e., low impact resistance, of these resins, the MBS or ABSM resin is blended with these resins. This blending is certainly effective for remarkably improving the impact resistance without degrading the transparency. The resultant resin composition may however suffer from the development of non-melted matters called fish eyes. Especially an extrudate derived from such a composition is liable to have unevenness on the surface thereof which impairs the appearance properties. Therefore, such a resin composition may be extremely restricted in its use.